Calcination and Wet Digestion as Sample Preparation Methods for Nickel Determination in Agronomic Stuffs: Technical Note

Nickel, although essential to plants, may be toxic to plants and animals. It is mainly assimilated by
food ingestion. However, information about the average levels of elements (including Ni) in edible
vegetables from different regions is still scarce in Brazil. The objectives of this study were to: (a)
evaluate and optimize a method for preparation of vegetable tissue samples for Ni determination; (b)
optimize the analytical procedures for determination by Flame Atomic Absorption Spectrometry
(FAAS) and by Electro-thermal Atomic Absorption (ETAAS) in vegetable samples and (c) determine
the Ni concentration in vegetables consumed in the cities of Lorena and Taubaté in the Vale do
Paraíba, State of São Paulo, Brazil. By means of the analytical technique for determination by ETAAS
or FAAS, the results were validated by the test of analyte addition and recovery. The most viable
method tested for quantification of this element was HClO4–HNO3 wet digestion. All samples but
carrot tissue collected in Lorena contained Ni levels above the permitted by the Brazilian Ministry of
Health. The most disturbing results, requiring more detailed studies, were the Ni concentrations
measured in carrot samples from Taubaté, where levels were five times higher than permitted by
Brazilian regulations.